Add ff_ prefix to data symbols of encoders, decoders, hwaccel, parsers, bsf.

None of these symbols should be accessed directly, so declare them as
hidden.

Signed-off-by: Mans Rullgard <mans@mansr.com>
(cherry picked from commit d36beb3f69)

libavcodec/libfaac.c

@@ -153,7 +153,7 @@ static const AVProfile profiles[] = {
     { FF_PROFILE_UNKNOWN },
 };
 
-AVCodec libfaac_encoder = {
+AVCodec ff_libfaac_encoder = {
     "libfaac",
     AVMEDIA_TYPE_AUDIO,
     CODEC_ID_AAC,